function loginout(User) {
    $.ajax({
        type:'POST',
        dataType:'json',
        contentType: 'application/json; charset=utf-8',
        url:'/loginout',
        data:JSON.stringify({
            "username":User
        }),
        success: function (data) {
            if (data.msg = 'ok') {
                alert("用户已下线")
            }
        },
        error: function (data) {
            alert("下线失败")
        }
    })
}